1cup(226 or 2 sticks) unsalted butter,, room temperature
2cups(400 g) granulated sugar
2teaspoonspure vanilla extract
4large eggs,, room temperature
2cups(475 ml) buttermilk,, room temperature
Swiss Meringue Buttercream
½cup(120 ml) egg whites* (about 4 eggs)
1cup(200 g) granulated sugar
1 ½cups(340 g or 3 sticks) unsalted butter,, room temperature, cubed
1teaspoonpure vanilla extract
Berries
5cupsmixed berries, sliced
2cupsmixed whole berries
Instructions
Vanilla Layer Cake
Preheat oven to 350° F. Butter and flour two 9-inch round cake pans to prevent cakes sticking to the pans (or use magic cake pan release).
Whisk together flour, baking powder, baking soda and salt in a medium bowl. Set aside.
In a large mixing bowl, beat butter and sugar with an electric mixer at medium speed until pale and fluffy. Beat in vanilla. Add eggs one at a time, beating well and scraping down the bowl after each addition.
Turn the mixer on low speed. Add about one-third of the flour mixture and mix until combined. Then add half of the buttermilk. Repeat. End with last third of flour.
Spread batter evenly in prepared cake pans. Tap pans on the counter several times to eliminate air bubbles. Bake until golden and a wooden pick inserted in center of cake comes out clean, 40 to 45 minutes. Cool in pan on a rack 10 minutes, then run a knife around edge of pan. Invert onto rack and cool completely, about 1 hour.
Swiss Meringue Buttercream
In the bowl of a stand mixer, whisk together egg whites and sugar until combined.
Place bowl over a hot water bath on the stove and whisk constantly until the mixture is no longer grainy to the touch (about 3 minutes).
Return bowl to the stand mixer and whisk on medium-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch, about 5-10 minutes).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth. The frosting may appear curdled at some point, keep mixing until smooth. Add vanilla and mix just until combined.
Assembly
Cut cake layers in half horizontally using a cake leveler or large serrated knife.
Place one layer onto your cake stand. Add 1/4 of the buttercream on top and spread roughly. Place 1/3 of berries over top of the buttercream. Repeat the process with the other layers, finishing with 2 cups of whole berries.
Notes
Tips for making Swiss meringue buttercream: Ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue won't stiffen. Frosting may appear curdled at some point. Keep mixing until smooth.Store triple berry layer cake in an airtight container (or securely covered) in the refrigerator for 3 days.